Oat cell carcinoma of the lung is a rapidly fatal disease. Regardless of therapy, nearly all patients die of metastases, suggesting that this tumor is a disseminated disease. This study evaluates combination chemotherapy with 3 active agents (cyclophosphamide, adriamycin, and VP 16-213) and immunotherapy with MER for its potential to increase response rate duration, or survival as well as its potential to alter drug toxicity. 34 patients have been entered. There have been 14 complete remissions, 10 partial remissions, 4 lesser responses, 3 patients without measurable disease, and 3 patients without response. 28 patients had received no prior therapy. 2 of these patients had no measurable disease, and the remaining 26 showed evidence of response. 24 of these 26 had either complete or partial response. 5 of 10 patients with partial response are still improving. Among 6 patients previously irradiated, 3 failed to respond, 2 died from hematologic toxicity, and 1 has no measurable disease. Whether the patient had limited or widespread disease had no appreciable effect on response rate or duration. MER has had no appreciable effect on response rate, duration, survival or drug toxicity. Toxicity was moderately severe including alopecia, nausea and vomiting and blood count suppression. Toxicities were manageable by dose modification. There were 3 drug-related deaths, and 2 patients died of arrhythmias MER toxicity included fever, chills, pain, local inflammation and weeping ulcers.